Using first-principles density functional theory and determinant quantum Monte Carlo methods, we show that Janus graphene nanoribbons with topological defect arrays ($m=2$) exhibit robust intrinsic ferromagnetism across widths $W=2\text{–}6$, with bandgaps exceeding $200\mathrm{meV}$ and stable ferromagnetic ground states. Notably, uniaxial tensile strain significantly enhances their ferromagnetic properties: at 25% strain, the Curie temperature increases to $222\mathrm{K}$—a fivefold improvement over unstrained systems and the highest reported for graphene-based nanoribbons. Strain also induces a reversible transition to a bipolar magnetic semiconductor, with spin-flipped valence and conduction band edges beyond 10% strain. This dual functionality—strain-enhanced ferromagnetism and strain-induced spin flip—stems from strain-modulated $p_z$ orbital hybridization and strong direct exchange interaction. Among these, $W=5$ Janus graphene nanoribbons emerge as potential candidates for room-temperature spintronic devices and strain-programmable quantum transport systems.

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• Magnetism
• Graphene
• Nanoribbon
• Monte Carlo methods